Method for producing ruthenium complexes

ABSTRACT

Ruthenium complexes of the formula I or IV 
     
       
         RuX 2 (═CH—CH 2 R)L 1 L 2   (I) 
       
     
     
       
         RuXY(═CH═CH 2 R)L 1 L 2   (IV) 
       
     
     where 
     X, Y are anionic ligands, 
     R is hydrogen or a substituted or unsubstituted C 1 -C 20 -alkyl radical or C 6 -C 20 -aryl radical and 
     L 1  and L 2  are, independently of one another, uncharged electron donor ligands, are prepared by 
     (a) reaction of RuX 3  with L 1  and L 2  in an inert solvent in the presence of a reducing agent and hydrogen and 
     (b) reaction with compounds of the formula II 
     
       
         R—C≡CH  (II) 
       
     
     where R is as defined above, in the presence or absence of water, and, if desired after isolation of the intermediate, with HY, [HL 1 ]Y or [HL 2 ]Y.

The present invention relates to processes for preparing rutheniumcomplexes which can be used, for example, as catalysts in metathesisreactions.

In its simplest form, olefin metathesis (disproportionation) is areversible, metal-catalyzed transalkylidenation of olefins by ruptureand re-formation of carbon-carbon double bonds. In the metathesis ofacyclic olefins, a distinction is made, for example, betweenself-metathesis, in which an olefine is converted into a mixture of twoolefins of different molar masses (for example conversion of propeneinto ethene and 2-butene), and cross- or co-metathesis, which describesthe reaction of two different olefins (for example of propene with1-butene to give ethene and 2-pentene). Further application areas ofolefin metathesis are syntheses of unsaturated polymers by ring-openingmetathesis polymerization (ROMP) of cyclic olefins and the acyclic dienemetathesis polymerization (ADMET) of α, ω-dienes. More recentapplications are the selective ring opening of cyclic olefins usingacyclic olefins, and also ring closure reactions (RCM) by means of whichunsaturated rings of different ring sizes can be produced, preferablyfrom α, ω-dienes.

Suitable catalysts for metathesis reactions are in principle homogeneousand heterogeneous transition metal compounds, in particular rutheniumcompounds.

Heterogeneous catalysts, for example molybdenum oxide, tungsten oxide orrhenium oxide on inorganic oxidic supports, have a high activity andregenerability in reactions of non-functionalized olefins but often haveto be pretreated with an alkylating agent to increase the activity whenfunctionalized olefins such as methyl oleate are used. Olefins havingprotic functional groups (such as hydroxyl groups, carboxyl groups oramino groups) lead to spontaneous deactivation of the heterogeneouscatalyst.

In recent years, increasing efforts have been made to preparehomogeneous catalysts which are stable in a protic medium and in thepresence of atmospheric oxygen. Catalysts which have been found to be ofparticular interest are specific ruthenium-alkylidene compounds. Suchcomplexes and processes of preparing them are known.

WO 93/20111 describes ruthenium- and osmium-carbene complexes for olefinmetathesis polymerization. The complexes have the structureRuX₂(═CH—CH═CR₂)L₂. Ligands L used are triphenylphosphine andsubstituted triphenyl-phosphine. The preparation is carried out, forexample, by reacting RuCl₂(PPh₃)₃ with suitable disubstitutedcyclopropenes as carbene precursors. However, the synthesis ofcyclopropene derivatives consists of a number of stages and is of littleinterest from an economic point of view.

Similar reactions are described in WO 96/04289. In addition, processesfor olefin metathesis polymerization are indicated.

The use of such catalysts for peroxide-crosslinking of ROMP polymers isdescribed in WO 97/03096.

WO 97/06185 likewise describes metathesis catalysts based onruthenium-carbene complexes. Apart from the above-described process,they can also be prepared by reaction of RuCl₂(PPh₃)₃ with diazoalkanes.However, handling diazoalkanes poses a safety risk, particularly whenthe process is carried out on an industrial scale.

In addition, the organometallic starting materials of the formulaRuCl₂(PPh₃)₃ have to be prepared from RuCl₃.3H₂O using a large excess oftriphenylphosphine. Subsequently, PPh₃ ligands are again lost by ligandexchange in the catalyst synthesis itself. The carbene precursors usedrequire multistage syntheses and do not have an unlimited shelf life.

Organometallics 1996, 15, 1960-1962 describes a process for preparingruthenium complexes in which polymeric [RuCl₂(cyclooctadiene)]_(x) ini-propanol is reacted with hydrogen in the presence of phosphine. Thiseliminates the necessity of phosphine exchange. An undefined mixture ofproducts is obtained. In addition, long reaction times are required whenstarting from a polymeric starting material. The cyclooctadiene presentin the organometallic starting material does not contribute to thereaction and is lost.

J. Chem. Soc. Commun. 1997, 1733-1734 describes the synthesis of amethylene complex RuCl₂(═CH₂)(PCy₃)₂ starting from dichloromethane andthe ruthenium polyhydride RuH₂(CH₂)₂(PCy₃)₂. However, theruthenium-polyhydride complex is difficult to obtain. Furthermore, longreaction times are required.

The known synthetic routes for preparing metathesis catalysts of thetype RuX₂(═CH—CH₂R)(PR′₃)₂ are uneconomical for the reasons mentioned.

It is an object of the present invention to provide processes forpreparing ruthenium alkylidene complexes of the type RuX₂(═CH—CH₂R)L¹L²or RuXY(═CH—CH₂R)L¹L², which processes lead, in a rapid andatom-economical reaction starting from readily available startingmaterials, to the desired products without ligand exchange. Theprocesses should also be inexpensive and give high yields under mildreaction conditions.

We have found that this object is achieved by a process for preparingruthenium complexes of the formula I

RuX₂(═CH—CH₂R)L¹L²  (I)

where

X is an anionic ligand,

R is hydrogen or a substituted or unsubstituted C₁-C₂₀-alkyl radical orC₆-C₂₀-aryl radical and

L¹ and L² are, independently of one another, uncharged electron donorligands, by

(a) reaction of RuX₃ with L¹ and L² in an inert solvent in the presenceof a reducing agent and hydrogen and, without isolation ofintermediates,

(b) subsequent reaction with compounds of the formula II

R—C≡CH  (II)

where R is as defined above, in the presence or absence of water.

This object is also achieved by a process for preparing rutheniumcomplexes of the formula IV

RuXY(═CH—CH₂R)L¹L²  (IV)

where

X, Y are identical or different anionic ligands,

R is hydrogen or a substituted or unsubstituted C₁-C₂₀-alkyl radical orC₆-C₂₀-aryl radical and

L¹ and L² are, independently of one another, uncharged electron donorligands, by

(a) reaction of RuX₃ with L¹ and L² in an inert solvent in the presenceof a reducing agent and hydrogen with compounds of the formula II

R—C≡CH  (II)

where R is as defined above, in the presence or absence of water, toform a compound of the formula V

RuXH(═C═CHR)L¹L²  (V)

where X, R, L¹, L² are as defined above,

(b) separation of the compound of the formula V from the reactionmixture and subsequent reaction with HY, (HL¹)Y or (HL²)Y in an inertsolvent with compounds of the formula II

R—C≡CH  (II)

where R is as defined above, in the presence or absence of water, and

(c) subsequent reaction with HY, [HL¹]Y or [HL²]Y.

It has been found that the above mentioned ruthenium complexes can beobtained in very good yields directly from RuX₃, preferablyRuCl₃.3(H₂O), by simple reaction with ligands L¹ and L², hydrogen andterminal alkynes of the formula II in the presence of reducing agentswithout isolation of intermediates. The ruthenium complexes have novinylic substituents on the carbene carbon atom. The starting materialscan be prepared inexpensively and are readily available.

To prepare the mixed-anion complexes of the formula IV, the intermediateof the formula V is isolated and subsequently reacted further. Thisenables different ligands X and Y to be introduced.

Firstly, the reaction of RuX₃ with the ligands L¹ and L² is carried outin an inert solvent in the presence of a reducing agent and hydrogen.Solvents which can be used are aromatics, heteroaromatics, cyclic oracyclic ethers. Preferred solvents are toluene, NMP, tetrahydrofuran,dialkyl ethers, glycol ethers and dioxane. Particular preference isgiven to tetrahydrofliran.

The reducing agent used can be any reducing agent which reduces Ru(III)to Ru(II) under the reaction conditions. The reduction is preferablycarried out using hydrogen in the presence of a metallic or nonmetallicreducing agent, preferably in the presence of an alkali metal, alkalineearth metal or transition metal, e.g. palladium or zinc, which ispresent in metallic form and/or can be applied to a support. Thealkaline earth metals, preferably magnesium, are preferably used in anactivated form. This activation can be achieved, for example, bycontacting with a chlorine-containing organic solvent. For example, in asingle-vessel reaction under an inert gas atmosphere, magnesium can beplaced in a diluted chlorine-containing organic solvent, for exampledichloroethane, and, after an induction period of from one second to 10hours, preferably from one minute to one hour, reacted with the solvent,RuX₃ and the ligands L¹ and L² under a hydrogen atmosphere. Thetemperature in this reaction step (a) is preferably from 0 to 100° C.,particularly preferably from 20 to 80° C., in particular from 40 to 60°C. The pressure is preferably from 0.1 to 100 bar, particularlypreferably from 0.5 to 5 bar, in particular from 0.8 to 1.5 bar. Thereaction is carried out for a time of preferably from 10 minutes to 100hours, particularly preferably from 1 hour to 10 hours. The molar ratioof both ligands L¹ and L² as a sum to the ruthenium salt used ispreferably 2-20:1, particularly preferably 2-5:1. After the reaction instep (a), the reaction mixture is reacted with a 1-alkyne, preferably atfrom −80 to 100° C., particularly preferably from −40 to 50° C., inparticular from −30 to 20° C. In this reaction, the molar ratio ofruthenium salt originally used to 1-alkyne is preferably from 1:1 to1:10. The reaction is preferably carried out at a pressure of from 0.1to 10 bar, particularly preferably from 0.8 to 1.5 bar, in particularfrom 1 to 1.4 bar, for a time of preferably from 30 seconds to 10 hours,particularly preferably from 1 minute to 1 hour.

To prepare the complexes of the formula I, isolation of the intermediateV is not necessary, but is possible. The further reaction in step (b) ispreferably carried out in the presence of water.

To prepare the mixed-anion complexes of the formula IV, the intermediateis isolated before the reaction in step (c), i.e. the reaction with HY,[HL¹]Y or [HL²]Y, preferably HY.

The reaction is usually complete after from 1 to 100 hours, preferablyfrom 3 to 10 hours, and gives metathesis catalysts in yields of up to95%, based on the ruthenium salt used. Suitable reactors are glass orsteel vessels in general, which may have to be pressure-resistant.

The reaction mixture obtained is preferably worked up by removingvolatile constituents under reduced pressure and extracting the solidresidue with an organic solvent such as pentane.

In the ruthenium complexes of the formulae I and IV, X is a monodentateanionic ligand, for example halogen, pseudohalogen, carboxylate,diketonate. X is particularly preferably halogen, in particular bromineor chlorine, especially chlorine. Particular preference is given tousing RuCl₃.3H₂O in the reaction.

In the ruthenium complexes of the formula IV, Y can be the same ligandas X. It is preferably a halogen different from X or is a carboxyl groupwhich is bound to a polymer or a support, thus making it possible to fixthe catalyst to a support. In the case of the intermediates of theformula V, the ligand X can also be replaced by means of salt metathesiswith MY, where M is an alkali metal or ammonium, preferably potassium.This also makes it possible to obtain product mixtures.

L¹ and L² are neutral electron donor ligands. Examples of such ligandsare amines, phosphines, arsines and stibines, preferably phosphines. L¹and L² are preferably selected from among phosphines of the formula III

PR¹R²R³  (III)

where R¹ and R² are independently phenyl radicals or organic, stericallyhindered radicals and R³ is hydrogen, a substituted or unsubstitutedC₁-C₂₀-alkyl radical or C₆-C₂₀-aryl radical or is as defined for R¹. Forthe purposes of the present invention, a “sterically hindered radical”is a radical which has a bulky structure. Examples of such radicals arei-propyl, tert-butyl, cyclopentyl, cyclohexyl, phenyl or menthyl.Preference is given to using a cyclohexyl radical as sterically hinderedradical. Particularly preferably, all three radicals R¹, R² and R³ aresterically hindered radicals or phenyl radicals, in particularcyclohexyl radicals. The radicals R¹, R and R³ can each bear suitablesubstituents. Examples of such substituents are C₁-C₆-alkyl radicals,preferably C₁-C₃-alkyl radicals, C₁-C₃-fluoroalkyl radicals, halogenatoms, nitro groups, amino groups, ester functions and acid functions,—OH, C₁-C₆-alkoxy groups or sulfonate groups. The radicals arepreferably not substituted.

The radical R is hydrogen or a substituted or unsubstituted C₁-C₂₀-,preferably C₁-C₆-alkyl radical or C₆-C₂₀-, preferably C₆-C₈-arylradical. As regards the substituents, what has been said above applies.Particularly preferred ruthenium complexes of the formula I areRuCl₂(═CH—CH₃)(PCy₃)₂ and RuCl₂(═CH—CH₂-Ph)(PCy₃)₂ where Cy is acyclohexyl radical and Ph is a phenyl radical.

The ruthenium complexes prepared according to the present invention canbe used as metathesis catalysts.

The invention is illustrated by the examples below.

EXAMPLE 1

Synthesis of the ethylidene complex RuCL₂(═CH—CH₃)(PCy₃)₂ fromRuCl₃.3H₂O and acetylene

50 mmol of activated magnesium were placed in 20 ml of abs. THF. Afteraddition of 8 mmol of RuCl₃.3H₂O, 31 mmol of tricyclohexylphosphine and80 ml of THF, the reaction mixture was stirred at 60° C. under 1 bar ofhydrogen for 6.5 hours. After cooling the reaction mixture to −30° C.,acetylene was passed in for about 10 seconds and the mixture was stirredfor another 5 minutes. The reaction mixture was subsequently admixedwith 0.5 ml of water, warmed to room temperature, the solvent wasremoved under reduced pressure, the solid residue was transferred to anextraction thimble and extracted with 20 ml of pentane in a Soxhlettextractor. The yield of analytically pure, red-violet solid isolated was5.3 g (88% of theory).

EXAMPLE 2

Synthesis of the complex RuCl₂(═CH—CH₂-Ph)(PCy₃)₂ from RuCl₃.3H₂O andphenylacetylene

After addition of 1.9 mmol of RuCl₃.3H₂O, 8 mmol oftricyclohexylphosphine and 0.5 ml of ClCH₂CH₂Cl to 50 mmol of activatedmagnesium in 25 ml of abs. THF, the reaction mixture was stirred at 60°C. under 1 bar of hydrogen for 6.5 hours. After the reduction, thereaction mixture was cooled to −40° C. and 1.9 mmol of phenylacetylenewere added dropwise, with vigorous gas evolution occurring. Afterstirring for 20 minutes at −40° C., the cooling was removed and, atabout 0° C., 7 mmol of water were added. After warming to roomtemperature, stirring was continued for another 10 minutes, the solventwas subsequently removed under reduced pressure and the residue wasextracted with 60 ml of toluene. The extract was evaporated to dryness,the crimson solid which remained was washed four times in successionwith 10 ml each time of pentane and then twice with 40 ml each time ofmethanol and was dried under reduced pressure. The yield of analyticallypure, crimson solid isolated was 1.2 g (76% of theory).

We claim:
 1. A process for preparing ruthenium complexes of the formulaI RuX₂(═CH—CH₂R)L¹L²  (I) where X is an anionic ligand, R is hydrogen ora substituted or unsubstituted C₁-C₂₀-alkyl radical or C₆-C₂₀-arylradical and L¹ and L² are, independently of one another, unchargedelectron donor ligands, by (a) reaction of RuX₃ with L¹ and L² in aninert solvent in the presence of a reducing agent and hydrogen and,without isolation of intermediates, (b) subsequent reaction withcompounds of the formula II R—C≡CH  (II)  where R is as defined above,in the presence or absence of water.
 2. A process for preparingruthenium complexes of the formula IV RuXY(═CH—CH₂R)L¹L²  (IV) where X,Y are identical or different anionic ligands, R is hydrogen or asubstituted or unsubstituted C₁-C₂₀-alkyl radical or C₆C₂₀-aryl radicaland L¹ and L² are, independently of one another, uncharged electrondonor ligands, by (a) reaction of RuX₃ with L¹ and L² in an inertsolvent in the presence of a reducing agent and hydrogen with compoundsof the formula II R—C≡CH  (II)  where R is as defined above, in thepresence or absence of water, to form a compound of the formula VRuXH(═C═CHR)L¹L²  (V)  where X, R, L¹, L² are as defined above, (b)separation of the compound of the formula V from the reaction mixtureand subsequent reaction with HY, (HL¹)Y or (HL²)Y in an inert solventwith compounds of the formula II R—C≡CH  (II) where R is as definedabove, in the presence or absence of water, and (c) subsequent reactionwith HY, [HL¹]Y or [HL²]Y.
 3. A process as claimed in claim 1, whereinL¹ and L² are selected from among phosphines of the formula IIIPR¹R²R³  (III) where R¹ and R² are, independently of one another, phenylradicals or organic, sterically hindered radicals and R³ is hydrogen, asubstituted or unsubstituted C₁-C₁₂-alkyl radical or C₆-C₂₀-aryl radicalor is as defined for R¹.
 4. A process as claimed in claim 3, wherein R¹and R² are selected from among i-propyl, tert-butyl, cyclopentyl,cyclohexyl, phenyl or menthyl.
 5. A process as claimed in claim 1,wherein X is halogen and Y is the same or different halogen or is acarboxyl group which is bound to a polymer or a support.
 6. A process asclaimed in claim 1, wherein the reduction with hydrogen is carried outin the presence of a metallic or nonmetallic reducing agent.
 7. Aprocess as claimed in claim 6, wherein the reducing agent used ismagnesium which is activated by contacting with a chlorine-containingorganic solvent.
 8. A process as claimed in claim 1, wherein thereaction in step (a) is carried out at a pressure in the range from 0.1to 100 bar and that in step (b) is carried out at a pressure in therange from 0.1 to 10 bar.
 9. A process as claimed in claim 1, whereinthe reaction in step (a) is carried out at from 0 to 100° C. and that instep (b) is carried out at from −80 to 100° C.
 10. A process as claimedin claim 1, wherein the solvent is selected from aromatics,heteroaromatics, cyclic or acyclic ethers.
 11. A process as claimed inclaim 1, wherein the ruthenium complexes of the formula I or IV are,after removal of volatile constituents from the reaction mixture,isolated in analytically pure form by extraction with an organicsolvent.
 12. A process as claimed in claim 2, wherein L¹ and L² areselected from among phosphines of the formula III PR¹R²R³  (III) whereR¹ and R² are, independently of one another, phenyl radicals or organic,sterically hindered radicals and R³ is hydrogen, a substituted orunsubstituted C₁-C₁₂-alkyl radical or C₆-C₂₀-aryl radical or is asdefmed for R¹.
 13. A process as claimed in claim 12, wherein R¹ and R²are selected from among i-propyl, tert-butyl, cyclopentyl, cyclohexyl,phenyl or menthyl.
 14. A process as claimed in claim 2, wherein X ishalogen and Y is the same or different halogen or is a carboxyl groupwhich is bound to a polymer or a support.
 15. A process as claimed inclaim 2, wherein the reduction with hydrogen is carried out in thepresence of a metallic or nonmetallic reducing agent.